1. Field of the Invention
This invention relates to shiftable change speed shifting mechanisms comprising selectively, axially movable gears and, in particular, relates to multiple countershaft transmissions utilizing resiliently yieldable shifting mechanism comprising selectively, axially movable main shaft gears having clutch teeth associated therewith and axially movable, resiliently biased clutch collars splined to the main shaft for selectively rotationally fixing said main shaft gears to said main shaft, said clutch collars having clutch teeth associated therewith for engaging the clutch teeth associated with said main shaft gears, wherein the spline teeth of one of the main shaft or clutch collar are of a constantly variable thickness to prevent or minimize undesired disengagement of an engaged mainshaft gear and clutch collar.
2. Description of the Prior Art
Change speed transmissions utilizing resiliently yieldable shifting mechanisms incorporating selectively, axially movable gears and, in particular, multiple countershaft, floating main shaft transmissions utilizing resiliently yieldable shifting mechanisms, are known in the prior art and may be seen by reference to U.S. Pat. Nos. 3,799,002; 3,910,131; 3,921,469; 3,924,484; and 3,983,979, all of which are assigned to the assignee of this invention and all of which are hereby incorporated by reference.
Briefly, the above mentioned multiple countershaft, floating main shaft transmissions utilizing resiliently yieldable shifting mechanisms comprise selectively, axially movable main shaft gears and axially movable clutch collars splined to the main shaft which are resiliently biased toward said main shaft gears and which are positively stopped from moving into engagement therewith until said main shaft gears are axially moved toward said clutch collars. The main shaft gears have clutch teeth associated therewith, preferably integral internal clutch teeth, and the clutch collars have integral external clutch teeth which are adapted to engage the clutch teeth associated with said main shaft gears. In the preferred embodiments of the above mentioned transmissions, various types of blockers are utilized to prevent engagement of the clutch teeth until the main shaft gear selected to be rotationally fixed to the main shaft is rotating at a synchronous speed with the main shaft. The main shaft gears are selectively, axially movable by shift fork mechanisms as is well known in the prior art and the shift fork mechanisms were manipulated by either a linkage mechanism or by a pressure fluid motor, such as an air cylinder, as is also well-known in the prior art.
While the above mentioned transmissions have proven to be highly desirable, especially for substantially simplifying shifting of the transmissions, in certain circumstances, especially in those transmissions utilizing air motor manipulated shift forks, the clutch teeth associated with certain engaged main shaft gears occasionally tended to undesirably disengage from the clutch teeth associated with the engaged clutch collar. This problem, which is sometimes referred to as "kick out", most often occurred during severe usage of the transmission. Such undesirable disengagement, or "kick out", while not completely understood, is believed to be caused by the engaged, selectively axially movable main shaft gear wobbling in respect to the axis of rotation of the main shaft which is believed to cause the main shaft gear to move axially against the shift fork and the bias of the shift cylinder until the clutch teeth associated therewith became disengaged from the clutch teeth associated with the clutch collar. The problem of undesirable disengagement, although not fully understood, is most often associated with those types of multiple countershaft transmissions wherein the main shaft gear is selectively axially moved toward engagement with a clutch collar, rather than with those types of transmissions wherein the main shaft gear is axially fixed with respect to the main shaft.